1. Field of the Invention
This invention, as a typical manner of recording, relates to a method of manufacturing a substrate used as a constitutional member for a liquid jet recording head which causes a condition change including the production of bubbles in liquid by heat energy, discharges the liquid from a discharge opening by the condition change to thereby form flying droplets, and causes the flying droplets to adhere to a recording surface to thereby accomplish recording of information such as characters and images. The invention also relates to substrate manufactured by the method, a liquid jet recording head formed by use of the substrate, and a liquid jet recording apparatus having the head.
2. Related Background Art
The non-impact recording methods have recently drawn increasing attention because the production of noise during recording is negligibly small. Among those methods, the so-called ink jet recording method (the liquid jet recording method) which is capable of highspeed recording and moreover can effect recording on plain paper without requiring the special process of fixation is a very promising recording method. Various systems using the ink jet recording method have heretofore been proposed and apparatuses which embody these systems have been desired, and some of them have been improved and commercialized and some are still under the process of being put into practical use.
Among them, the liquid jet recording methods described, for example, in Japanese Laid-Open Patent Application No. 54-59936 (corresponding U.S. Pat. Nos. 4,723,129, 4,740,796) and German Laid-Open Patent Application (DOLS) No. 2843064 have a feature differing from that of the other liquid jet recording methods in that heat energy which is energy to be used for discharging liquid is caused to act on liquid to thereby obtain a motive force for liquid droplet discharge.
That is, in the typical example of recording methods disclosed in the above-mentioned publications, liquid subjected to the action of the heat energy causes a condition change involving a steep increase in volume, and by an action of force based on the condition change, liquid is discharged as a droplet from a discharge opening (hereinafter referred to as the orifice), for example, provided at the fore end of a recording head unit and flies and adheres to a recording medium, whereby recording of information is accomplished
The liquid jet recording method disclosed above can not only be very effectively applied to the so-called drop-on demand recording method, but also can be easily realized by providing the recording head unit with highly dense multiple orifices over the full line width thereof corresponding to the recording region of the recorded member and therefore, has an advantage that images of high resolution and high quality can be obtained at a high speed.
An embodiment of the recording head of an apparatus applied to the above-described recording system is provided with a liquid discharge portion having an orifice provided to discharge ink as droplet therethrough and an ink liquid path provided with a heat-acting portion as a portion communicating with the orifice and causing heat energy to be used for discharging ink to act on the ink, and an electrothermal transducer provided corresponding to the heat-acting portion as means for generating the heat energy.
A typical example of this electro-thermal transducer comprises a pair of electrodes, and a heat generating resistance layer connected to these electrodes and a heat generating region (a heat generating portion) being constituted at a position corresponding to the portion between the electrodes. The heat generating resistance layer and electrodes are generally formed in the surface portion of the base plate of the ink jet recording head as a layer. An example of the prior-art construction of the base plate in which such an electro-thermal transducer is formed is shown in FIGS. 1A and 1B of the accompanying drawings The example of the prior art will hereinafter be described with reference to these figures.
FIG. 1A is a fragmentary plan view showing the vicinity of an electro-thermal transducer in a substrate (hereinafter also referred to as the base plate) constituting an ink jet recording head, and FIG. 1B is a fragmentary cross-sectional view of a portion indicated by dot-and-dash line XY in FIG. 1A.
In these figures, the base plate 101 is formed by a lower layer 106, a heat generating resistance layer 107, electrodes 103, 104, a first upper protective layer 108, a second upper protective layer 109 and a third upper protective layer 110 successively laminated on a supporting member 105.
The heat generating resistance layer 107 and electrodes 103 and 104 are patterned into a predetermined shape by etching. That is, in the other portions than the portion being constituted the heat generating region 102, they are patterned almost into one and the same shape, and in the portion, being constituted the heat generating region 102, the electrodes are not laminated on the heat generating resistance layer 107, but the heat generating resistance layer 107 constitutes a heat generating portion 111. The first upper protective layer 108 and the third upper protective layer 110 are laminated over the whole surface of the base plate 101, while the second upper protective layer 109 is patterned so as not to be laminated on the heat generating region 102.
The material to be used for forming each layer provided in the surface portion of the base plate formed as described above is suitably chosen based on characteristics such as heat-resisting property, liquid-resisting property, heat conductivity and insulativeness required corresponding to respective portion of layers The main function of the first upper protective layer 108 in the above-described example of the prior art is to insulate the common electrode 103 from the selected electrode 104, the main function of the second upper protective layer 109 is to prevent the permeation of liquid and resist the liquid, and the main function of the third upper protective layer 110 is to reinforce the liquidresisting property and mechanical strength.
Now, of the first and third protective layers 108 and 110 lying on the upper layer of the heat generating region (hereinafter also referred to as heater portion for discharging) 102, the third protective layer 110 is in contact with ink, and with regard to the defects of the film forming these layers, care must be particularly taken of insulativeness or the like. Pin-holes and dust in the film may be mentioned as the defects of the film, and with regard to pin-holes, for example, as shown in JP Laid-Open Patent Application No. 60-157872 (corresponding U.S. Pat. No. 4,777,494), could be dissolved by anode-oxidizing the ground of the film portion, but the entry of dust into the film could not be sufficiently dissolved.
That is, in the ink jet system in which heat is caused to act, the first and third protective layers 108 and 110 need to be formed thin (for example, 3 .mu.m at greatest) in view of efficiency of heat conductivity and accordingly, as the forming method therefor the vacuum accumulation method has been preferred. The vacuum accumulation method, because of its system, cannot prevent the entry of dust into the film with an acceptable reliability. This is because, for example, when a vacuum container is subject to vacuum, especially after film formation, part of the film which has peeled from the wall of the vacuum container adheres to the base plate and becomes dust in the film.
In the case of a base plate on which about twenty-four heater portions for discharging are formed, the probability with which the base plate becomes unsatisfactory due to the entry of dust is not extremely high and therefore, there will be little problem if base plate entered dust is dealt with as unsatisfactory. However in the case of, for example, a base plate on which one thousand or more heater portions for discharging are formed, the entry of dust into a base plate may become great and therefore many problems arise. In either case, due to the entry of dust in the film, durability of the head itself may become bad. That is, if dust is present in the film, the dust will separate from within the film due to the action of force during the formation of a bubble for discharging ink and it will develop a pin-hole. The ink may penetrate into such pin-hole and come into contact with the heater portion for discharging and react therewith, whereby the heater portion for discharging may be disconnected.
Thus, the presence of defects in the protective layers of the heat generating portion due to the entry of dust into the film, reduces the durability of the head remarkably. Again, in such a case, if the base plate is one on which for example, about twenty-four heater portions for discharging are formed, the probability with which the base plate becomes unsatisfactory is low and therefore, it will pose no problem in terms of yield to regard base plate entered dust as being unsatisfactory, but in the case of, for example, a base plate on which one thousand or more heater portions for discharging are formed, the probability of heater portions for discharging which suffer from the entry of dust into a base plate will become great and if all these are regarded as being unsatisfactory, it will cause a reduction in yield.
On the other hand, when in the liquid jet recording head as described above, short-circuiting has occurred between wirings during the manufacturing process, the short-circuited wiring portion has been cut by the use of a laser beam to thereby separate the wirings from each other, but when a laser beam is thus used, as shown in FIGS. 2A-1 and 2B-1 of the accompanying drawings, a damage has been imparted to the heat generating resistance layer 202 on the support member 201 of the substrate for recording head to form a large hole (recess) 206. Then, in order to protect the wirings from recording liquid (ink), an upper protective layer 204 is formed near the wirings 203 by a film making method such as the sputtering method, but in the location of this large hole 206, the wiring 203 could not be sufficiently covered with the upper protective layer 204.
Therefore, as indicated by arrow K in FIG. 2B-2 of the accompanying drawings, during the use, the ink will sometimes permeate into the portion in which the hole 206 has been formed to thereby corrode the electrodes 203. This has sometimes led to the disconnection of the wirings. The reference numeral 205 designates that portion of the electrode which has been corroded by the ink.
So, an attempt has been made to further provide a second upper protective layer on the protective layer 204, but in the case of such a large hole 206 (usually having a depth of 1 .mu.m or more), bubbles have collected there or have been repelled by the protective film, and it has been the case that the wirings cannot be covered well even with the second upper protective layer. Also, aluminum has heretofore been generally used as the material for the wirings, and in order to prevent the above-described corrosion, attempts have been made to find electrically conductive materials other than aluminum, but there has not been yet found an anticorrosive conductive materials optimum in respect of manufacturing cost, workability and resistivity characteristic.
Thus, heretofore, it has happened that the ink permeates from the portion in which the wirings have been cut by a laser beam and the wirings are corroded and thereby disconnected, and this has sometimes reduced the reliability of the recording head.